f-Element Half-Sandwich Complexes: A Tetrasilylcyclobutadienyl–Uranium(IV)–Tris(tetrahydroborate) Anion Pianostool Complex |
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| Authors: | Josef T Boronski Dr Laurence R Doyle Dr John A Seed Dr Ashley J Wooles Prof Dr Stephen T Liddle |
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| Institution: | Department of Chemistry and Centre for Radiochemistry Research, The University of Manchester, Oxford Road, Manchester, M13 9PL UK |
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| Abstract: | Despite there being numerous examples of f-element compounds supported by cyclopentadienyl, arene, cycloheptatrienyl, and cyclooctatetraenyl ligands (C5–8), cyclobutadienyl (C4) complexes remain exceedingly rare. Here, we report that reaction of Li2{C4(SiMe3)4}(THF)2] ( 1 ) with U(BH4)3(THF)2] ( 2 ) gives the pianostool complex U{C4(SiMe3)4}(BH4)3]Li(THF)4] ( 3 ), where use of a borohydride and preformed C4-unit circumvents difficulties in product isolation and closing a C4-ring at uranium. Complex 3 is an unprecedented example of an f-element half-sandwich cyclobutadienyl complex, and it is only the second example of an actinide-cyclobutadienyl complex, the other being an inverse-sandwich. The U−C distances are short (av. 2.513 Å), reflecting the formal 2− charge of the C4-unit, and the SiMe3 groups are displaced from the C4-plane, which we propose maximises U−C4 orbital overlap. DFT calculations identify two quasi-degenerate U−C4 π-bonds utilising the ψ2 and ψ3 molecular orbitals of the C4-unit, but the potential δ-bond using the ψ4 orbital is vacant. |
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| Keywords: | Cyclobutadienyl Koordinationsverbindungen Halbsandwich-Komplexe Tetrahydroborat Uran |
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